Allylphosphonic acid esters are useful intermediates to form compounds having a variety of applications. For example, allylphosphonic acid esters are useful as starting materials for the synthesis of medicinal products and agricultural chemicals. Allylphosphonic acid ester derivatives may also be converted into a fire-retardant polymer by copolymerizing with styrene, ethylene, vinyl chloride and the like.
Allylphosphonic acid esters are also useful intermediates to form allylphosphonic acids. Allylphosphonic acids have a variety of applications such as, for example, a starting material to prepare water-soluble polymers which have utility as water treatment additives.
Heretofore, allylphosphonic acid esters have been prepared by reaction of an allyl halide and trialkyl phosphite by either of three processes. The Michaelis-Arbusov reaction using allyl or methyallyl chloride was carried out in the absence of a catalyst under rigorous reaction conditions with moderate yields. It was not possible to obtain any reaction between allyl chloride and triethyl phosphite at normal pressure. Where the reaction was carried out under pressure, the yield obtained using a 10-molar excess of allyl chloride was at the most 53% according to A. E. Arbusov et al., Izvest. Akad. Nauk. SSSR, Otdel. Khigm, Nauk. 1951, 714.
In a second process according to Japan Kokai No. 73-75,528, the direct reaction of an allyl halide compound with a trialkyl phosphite compound was accomplished in the presence of a nickel halide catalyst at a high temperature. Another process involved heating an allyl halide compound and a trialkyl phosphite compound in the presence of an alkyl amine in a sealed tube. This process is described in detail in Compt. Rend 259:2244 (1964).
In the latter two processes, conversion of alkyl halide and trialkyl phosphite into the desired allylphosphonic acid ester is low and yields are not readily reproducible. The reaction product is generally a mixture of the allylphosphonate ester and the corresponding alkylphosphonate ester. The formation of the latter being the result of a side reaction which can drastically lower the yield of the desired allyl diester. The difficulty in separating the allyl ester and alkyl ester products may further threaten the yield of the desired allyl ester since the boiling points of the esters may be very close, such as, for instance, in the case of the allylphosphonic dimethyl ester and the methylphosphonic dimethyl ester.
U.S. Pat. No. 4,633,005 issued to David Nalewajek et al., discloses a process for preparing allylphosphonic esters in improved yields which process involves reacting an allyl halide with the appropriate phosphite in the presence of a phosphinated d.sup.8 -transition metal catalyst. This process is costly, however, since it requires the use of an expensive and complex phosphinated catalyst.
U.S Pat. No. 4,017,564 issued to Gunter Arend et al., discloses a process for the production of allylphosphonic acid esters by reacting allyl chloride with trialkyl phosphites at temperatures of from 80.degree. to 160.degree. C. in the presence of an avalent and/or monovalent nickel catalyst. The reference points out the inferiority of divalent nickel catalysts to produce allylphosphonate esters in good yield.
Accordingly, it is an object of the invention to provide a practical and efficient process for forming allylphosphonic acid esters in high selectivity and yield using a simple, inexpensive divalent nickel catalyst. It is also an object of this invention to provide an improved process for forming the allylphosphonate esters in the presence of a divalent nickel catalyst which process reduces formation of the alkylphosphonate esters, thereby forming an allyl ester product having increased purity.
Other objects will be evident from the ensuing description and appended claims.